1. Field of the Invention
This invention relates to a pipe scraper which removes a portion of the exterior surface of a pipe prior to affixing the pipe to a coupling.
2. Description of Prior Art
It is often necessary to remove a portion of the exterior surface of a pipe prior to welding or otherwise affixing the pipe to a coupling. In an electrofusion process for joining plastic pipes, such as those constructed of polyethylene, it is an absolute requirement. Removal of a portion of the exterior surface of the pipe eliminates oxidation of and impurities in the exterior surface of the pipe, and helps ensure a trouble-free joint.
The exterior surface of a pipe should be scraped to a depth of no more than 10 percent of the overall thickness of the pipe wall. Generally, with smaller diameter pipe, such as 1/2 inch CTS to one inch IPS, removal of about 0.005 inch of the pipe (0.010 on the diameter) will result in good fusion adhesion with a minimum loss of pipe wall thickness. A scrape exceeding 10 percent of wall thickness can compromise the strength of the pipe, while failure to scrape the entire perimeter of the pipe can result in poor fusion adhesion.
A problem often arises when scraping a pipe having an oval cross section. Scraping an oval pipe can result in a scrape exceeding 10 percent of wall thickness on some portions of the pipe, while other portions of the pipe are left entirely unscraped. To scrape such a pipe with a scraper which does not compensate for ovality of a pipe requires complex adjustment of scraper blade depth, which is time consuming, craft sensitive and increases the likelihood of a poorly fused and thus weakened joint.
U.S. Pat. No. 4,825,543 discloses a scraping tool for scraping the exterior surface of polyethylene pipes prior to use in an electrofusion process. The apparatus of the '543 patent includes two curved members which share a common pivot point. The curved members are pivotally opened to accept a pipe, and pivotally closed about the pipe prior to the scraping process. A bell-crank connection positioned at the non-pivot ends of the curved members maintain the apparatus in a closed position. Rollers positioned on the interior of each curved member urge the pipe against a scraping blade mounted on the interior of one of the curved members. The many moving components of the apparatus of the '543 patent increase both the relative cost and likelihood of malfunctioning of such apparatus.
U.S. Pat. No. 5,285,576 discloses a tool for grooving or cutting a pipe. An end of a pipe is inserted in the tool and is supported at two points by rollers. A spring urges a cutting wheel against a surface of the pipe and cuts or grooves the pipe as the tool is rotated with respect to the pipe. The '576 patent provides no teachings regarding how to achieve a uniform scrape of an oval pipe.
U.S. Pat. Nos. 3,117,375 and 3,651,569 disclose tools for cutting pipes or cables. Neither such patent addresses the problems associated with scraping an oval pipe to a uniform depth.
Thus it is apparent that a reliable and relatively economical tool for scraping round and oval pipes to a precise and uniform depth, particularly in the electrofusion industry, is highly desirable.